Mobile radio technology is subject to rapid development. At the moment, work is being carried out on the standardization of the so-called UMTS mobile radio standard (“Universal Mobile Telecommunications System”) for the third generation of mobile radios. According to the current state of UMTS standardization, the intention is to subject data to be transmitted via a radio-frequency channel to channel coding, with convolutional codes being used, in particular, for this purpose. The channel coding process results in the data to be transmitted being coded in a redundant manner, thus making it possible to recover the transmitted data more reliably at the receiver end. The code which is in each case used for the channel coding is characterized by its code rate r=k/n, where k denotes the number of data or message bits to be transmitted, and n denotes the number of bits which are present after the coding process. The lower the coding rate, the more powerful the code generally is. One problem which is associated with the coding process is, however, that the data rate is reduced by the factor r.
In order to match the data rate of the coded data stream to the respectively possible transmission rate, rate matching is carried out in the transmitter, in which process bits are either removed from the data stream, or are duplicated in the data stream, in accordance with a specific pattern. The removal of bits is referred to as a “puncturing”, and the duplicating of bits is referred to as “repetition”.
According to the current state of UMTS standardization, it is being proposed that a rate matching algorithm will be used which carries out puncturing using an approximately regular puncturing pattern; that is to say, the bits to be punctured are distributed equidistantly over the coded data block which is in each case to be punctured.
Furthermore, it is known that the bit error rate (BER) at the edge of a correspondingly coded data block decreases during the convolutional coding process. It is likewise known that the bit error rate can be changed locally within a data block by irregularly distributed puncturing. This knowledge has been used to find heuristically a puncturing pattern after whose use all the bits in the punctured data block will have a bit error rate corresponding to their respective importance. However, a procedure such as this is not practicable for UMTS mobile radio systems since a generally applicable algorithm is required here, which gives the desired results for any number of bits in a data block to be punctured, for any puncturing rate.
The present invention is, thus, directed toward a method for adapting the data rate of a data stream in a communications apparatus, as well as a corresponding communications apparatus, which leads to a satisfactory bit error rate and, in particular, can be used in mobile radio systems which use convolutional coding.